Journal of Middle East Applied Science and Technology (JMEAST) ISSN (Online): 2305-0225 Issue 24, Sept. 2014, pp. 803-809 803 An Experimental Investigation on the Effects of Operating Conditions on the Efficiency of a Flat-Plate Solar Collector Mozhdeh Khorramifard 1 , Masoud Haghshenasfard 2 , and S. Gholamreza Etemd 3 Abstract—In this study, experimental investigations have been carried out for obtaining the thermal efficiency of a flat plate solar collector. Thermal efficiency of the collector was plotted against reduced temperature parameter and the effects of the ambient temperature, operating temperature, and radiation intensity on the collector thermal performance have been investigated. The results showed that the thermal efficiency increases by increasing the ambient temperatureand decreasing the inlet temperature. It is shown that the the collector has a better performance under the lower operational temperatures. Keywords—solar energy, solar collector, efficiency, radiation intensity. INTRODUCTION ENERGY crisis has made countries behave differently towards issues related to energy in recent years [1]. Therefore, replacing fossil fuels with renewable energy, especially solar energy,istaken into consideration.Solar powersare more expensivecompared to other conventional energy sources like natural gas, but their overall cost continues to decrease with a quick rate. 1 MozhdehKhorramifard, Department of Chemical Engineering, Isfahan University of Technology, 84156-83111, Isfahan, Iran (e- mail:m_khorramifard@yahoo.com ) 2 MasoudHaghshenasfard, Department of Chemical Engineering, Isfahan University of Technology , 84156-83111, Isfahan, Iran (Correspondingauthor,Phone: +98-311-3915647, Fax: +98-311-3912677e- mail:haghshenas@cc.iut.ac.ir ) 3 S. Gh. Etemad, Department of Chemical Engineering, Isfahan University of Technology , 84156-83111, Isfahan, Iran (e- mail:etemad@cc.iut.ac.ir ) According to official statistics, more than 200 sunny days is reported in Iran, thus using solar energy is very affordable.The amplification of affordable, and inexhaustible and clean solar energy technologies will have huge longer-term benefits.Solar hot water system isone of the main applications of solar energy, whichuse sunlight to heat water.The most common types of these systems are flat plate solar collectors, evacuated tube collectors, and unglazed plastic collectors [2-3].Flat plate solar collectors are the most common type and consist of an absorber plate, transparent cover, working fluid, heat insulating backing, and the risers. The risers are installedon theabsorbing plate. Heat is transferred to the heat-transfer fluid which in turn feeds the hot water system.Working fluid is usually circulated through the risers to remove heat from the absorber and transfer to the water tank [4-5]. Pipes exposed to outdoor air should be properly insulated. The fluid flow and temperature distribution in the solar orbit are managed using a controller system. Recently, many experimental and numerical studies were performed to the flat plat solar collectors and various factors such as glazing effects, absorption coefficient, and collector tilt,have been investigated[6-10]. Effects of position of the flat plate reflectors on thermal efficiency of solar collectors are investigated by Kostic et al.[11].The optimal position of reflector has been determined and the results showed that the thermal efficiencyof collector with reflectors in optimal position is higher than thermal efficiency of collector without reflectors.